Systems and methods for determining location of an access needle in a subject

ABSTRACT

Systems and methods for epicardial electrophysiology and other procedures are provided in which the location of an access needle may be inferred according to the detection of different pressure frequencies in separate organs, or different locations, in the body of a subject. Methods may include inserting a needle including a first sensor into a body of a subject, and receiving pressure frequency information from the first sensor. A second sensor may be used to provide cardiac waveform information of the subject. A current location of the needle may be distinguished from another location based on an algorithm including the pressure frequency information and the cardiac waveform information.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority under 37 CFR §1.78(a) to U.S.Provisional Application Ser. No. 61/482,527 filed on May 4, 2011, thecontents of which are incorporated herein by reference in theirentirety.

The present application is related to the following applications, ofwhich all of the disclosures of the following applications are herebyincorporated by reference herein in their entireties:

PCT International Application Serial No. PCT/US2008/056643, filed Mar.12, 2008, entitled, “Access Needle Pressure Sensor Device and Method ofUse” and corresponding U.S. patent application Ser. No. 12/530,830 filedSep. 11, 2009;

PCT International Application Serial No. PCT/US2008/056816, filed Mar.13, 2008, entitled, “Epicardial Ablation Catheter and Method of Use” andcorresponding U.S. patent application Ser. No. 12/530,938 filed Sep. 11,2009;

PCT International Application Serial No. PCT/US2008/057626, filed Mar.20, 2008, entitled, “Electrode Catheter for Ablation Purposes andRelated Method Thereof” and corresponding U.S. patent application Ser.No. 12/532,233 filed Sep. 21, 2009;

PCT International Application Serial No. PCT/US2010/033189, filed Apr.30, 2010, entitled “Access Trocar and Related Method Thereof”;

PCT International Application Serial No. PCT/US2008/082835, filed Nov.7, 2008, entitled, “Steerable Epicardial Pacing Catheter System PlacedVia the Subxiphoid Process,” and corresponding U.S. patent applicationSer. No. 12/741,710 filed May 6, 2010;

PCT International Application Serial No. PCT/US2010/061413, filed Dec.21, 2010, entitled “System For Femoral Vasculature Catheterization andRelated Method; and

PCT International Application Serial No. PCT/US2011/025470, filed Feb.18, 2011.

BACKGROUND OF THE INVENTION

Interest in epicardial (outer wall of the heart) treatment ofventricular cardiac arrhythmias has grown significantly withinelectrophysiology. The thickness of the myocardial wall makes itdifficult to treat all heart rhythm problems endocardially (from insidethe heart). Although early (pre-reperfusion era) data suggested thatepicardial ventricular tachycardia (VT) occurred in a minority ofpatients, recent (non-ischemic VT and rapid reperfusion era) datasuggests that about 70% of VT patients have epicardial substrates forthe disease. Several studies have suggested that epicardial ablationprocedures are not only a viable second line of defense when endocardialmethods fail, but that epicardial procedures should be performed inconcert with all endocardial treatments to guarantee the greatestprobability of treatment success of both ventricular tachycardia (whichkills 500,000 Americans per year) and atrial fibrillation (which is thelargest cause of strokes in the U.S.). The epicardial surface is alsoconsidered to be an important potential therapeutic location for drugand cell delivery and as well as for heart failure therapy.

The ability to gain minimally invasive access to the heart's outer wallfor ablation and other therapies has done much to promulgate theadoption of epicardial strategies.

However, conventional types of guidance methods lead to an unacceptableand high risk of perforations of the RV tissue. For instance, Sosa andScanavacca had an initial perforation rate of 8%, which decreased to4.5% with experience. Others using this approach have experienced 12%unsuccessful pericardial access, with pericardial effusion in 13 of 35cases and one death from complications. Still another study suggestedthat 10 to 20% of all patients undergoing pericardial access forepicardial ablation using the methods described above experiencedeffusions due to some level of ventricular perforation.

Therefore, it is a goal of an aspect of an embodiment of the presentinvention to, among other things, improve the method of access andreduce the risks of its use.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present invention may find applicability in systems andmethods such as those described in, for example, epicardialelectrophysiology and other procedures in which the location of anaccess needle may be inferred according to the detection of differentpressure frequencies in separate organs, or different locations, in thebody of a subject.

An aspect of an embodiment of the present invention may provide, amongother things, continuous measurements of the pressure-frequencycharacteristics across the different regions of the thorax. As discussedfurther herein, data of that type may be used, for example, to determinehow the thoracic pressure-frequency waveform changes upon gainingproximity of and then traversing through the parietal pericardialmembrane. The inventors have found that it can further be determined ifthe transition to a two-component (intubation+heartbeat) signal wassmooth and gradual, or more abrupt in nature.

Aspects of the present invention may further provide, among otherthings, improved instrumentation to collect continuous segments ofpericardial and non-pericardial pressure-frequency data in vivo, incontrast to the discrete-location measurements. In particular, anexemplary approach incorporates a high precision fiber-optic sensor intothe distal tip of the access needle, which may replace the strain gaugesensor acted on by a fluid column within a stationary sheath in analternative embodiment.

Further aspects of the invention may provide, among other things, ananalysis algorithm, method, technique and system designed to processpressure-frequency data so as to identify when the needle's tip hadsafely entered, for example, the pericardial space.

An aspect of an embodiment of the present invention may, among otherobjects, reduce the clinical risks associated with minimally invasivesubxiphoid access, and thus improving the reliability, safety andefficacy of it in the epicardial treatment of cardiac arrhythmias andother clinical treatment paths involving the pericardium and epicardialsurface.

According to aspects of the invention, methods for inferring thelocation of a needle in a subject may include one or more steps ofinserting a needle including a first sensor into a body of a subject,receiving cardiac waveform information of the subject from a secondsensor, and receiving pressure frequency information from the firstsensor. Embodiments may include distinguishing, by a computer processor,a current location of the needle from another location and/ordistinguishing the transition of the needle from a first location to asecond location, based on an algorithm including the pressure frequencyinformation and the cardiac waveform information.

Embodiments may include determining a reference phase based on thecardiac waveform information and/or determining a test phase based onthe pressure frequency information. In embodiments, the distinguishingof location, and/or movement, of the needle may be based on the pressurefrequency information from the test phase and the cardiac waveforminformation from the reference phase.

In embodiments, the distinguishing of location, and/or movement, of theneedle may include comparing the algorithm results of the pressurefrequency information and the cardiac waveform information to aplurality of predetermined threshold values.

In embodiments, the combining of the pressure frequency information andthe cardiac waveform information may include phase sensitive detectionand matched filtering.

In embodiments, the combining of the pressure frequency information andthe cardiac waveform information may include integrating the pressurefrequency information.

In embodiments, the reference phase may be a cardiac phase of thesubject immediately preceding the test phase. In embodiments, thecardiac waveform information may include information derived from aplurality of cardiac phases of the subject.

In embodiments, the cardiac waveform information may include at leastone of ventricle pressure, arterial pressure, pulse oximetry, andelectrocardiogram (ECG) signals.

In embodiments, the current location may be a non-pericardial locationand the other location may be a pericardial location, or vice-versa. Inembodiments, at least one of the current location and the other locationmay be a thorax of the subject.

Embodiments may also include distinguishing between a location remotefrom the pericardium, a location close to or in contact with thepericardium, and a location inside the pericardium.

Embodiments may also include identifying a location within ventriculartissue of the subject or inside the interior of the heart of thesubject.

According to further aspects of the invention systems for accessing oneor more locations of a subject may also be provided. Such systems mayinclude, for example, a needle having a distal end and a proximal endand a first sensor in communication with the needle for sensing pressurefrequency in the one or more locations of the subject. Embodiments mayfurther include a processor configured to perform various steps, such asthose discussed above. For example, in embodiments, a processor may beconfigured to receive cardiac waveform information of the subject from asecond sensor and receive pressure frequency information from the firstsensor. The processor may be further configured to distinguish a currentlocation of the needle from another location, and/or the movement of theneedle from one location to another, based on an algorithm including thepressure frequency information and the cardiac waveform information.

The processor may be further configured to determine a reference phasebased on the cardiac waveform information, and/or determine a test phasebased on the pressure frequency information. The processor may befurther configured to distinguish the location and/or movement of theneedle based on the pressure frequency information from the test phaseand the cardiac waveform information from the reference phase.

In embodiments, the processor may be configured to compare the algorithmresults of the pressure frequency information and the cardiac waveforminformation to a plurality of predetermined threshold values.

In embodiments, the processor may be configured to combine the pressurefrequency information and the cardiac waveform information using phasesensitive detection and matched filtering.

In embodiments, the processor may be configured to integrate thepressure frequency information as part of the combining of the pressurefrequency information and the cardiac waveform information.

In embodiments, the processor may be configured such that the referencephase is a cardiac phase of the subject immediately preceding the testphase.

In embodiments, the processor may be configured such that the cardiacwaveform information includes information derived from a plurality ofcardiac phases of the subject.

In embodiments, the processor may be configured to receive cardiacwaveform information including at least one of ventricle pressure,arterial pressure, pulse oximetry, and electrocardiogram (ECG) voltages.

In embodiments, the processor may be configured to distinguish between anon-pericardial location and a pericardial location, a pericardiallocation and a thorax of the subject, and/or between a pericardiallocation and a location within ventricular tissue of the subject orinside the interior of the heart of the subject.

According to further aspects of the invention, a device for inferringthe location of a needle in a subject may be provided including a firstinput configured to receive pressure frequency information from a firstsensor and a second input configured to receive cardiac waveforminformation of the subject from a second sensor. In embodiments, thefirst sensor may be disposed proximate to a distal end of the needle.Embodiments may further include a processor in communication with thesensors, the processor configured to perform steps such as thosediscussed above. For example, the processor may be configured to receivecardiac waveform information of the subject from the second sensor viathe second input and/or to receive pressure frequency information fromthe first sensor via the first input. In embodiments, the processor maybe configured to distinguish a current location of the needle fromanother location, and/or distinguish movement of the needle from a firstlocation to a second location, based on an algorithm including thepressure frequency information and the cardiac waveform information.

In embodiments, the processor may be further configured to determine areference phase based on the cardiac waveform information, and determinea test phase based on the pressure frequency information. Thedistinguishing may be based on the pressure frequency information fromthe test phase and the cardiac waveform information from the referencephase.

Additional features, advantages, and embodiments of the invention may beset forth or apparent from consideration of the following detaileddescription, drawings, and claims. Moreover, it is to be understood thatboth the foregoing summary of the invention and the following detaileddescription are exemplary and intended to provide further explanationwithout limiting the scope of the invention claimed. The detaileddescription and the specific examples, however, indicate only preferredembodiments of the invention. Various changes and modifications withinthe spirit and scope of the invention will become apparent to thoseskilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the detailed description serve to explain the principlesof the invention. No attempt is made to show structural details of theinvention in more detail than may be necessary for a fundamentalunderstanding of the invention and various ways in which it may bepracticed. In the drawings:

FIG. 1 shows a chart of novel software algorithm, method, and techniquesteps. Two parallel paths denote the analysis of the reference waveform(left) and the input needle waveform (right).

FIGS. 2A-2B show the ECG waveform segmentation. An example ECG waveform(FIG. 2A solid line) is shown, as well as the resulting segmentationpoints at the R wave (FIG. 2A dotted line). The processed ECG accordingto the algorithm, method, and technique in FIG. 1 is shown as well inFIG. 2B.

FIG. 3 shows the algorithm and method signal analysis. Pericardial(left) and non-pericardial (right) examples of the analysis of cardiacsignal segments. Current cardiac segment (G), previous cardiac segmentinterpolated and normalized (B), and multiplied signals prior tointegration (R).

FIG. 4 shows the average (dimensionless) test output values for all 98non-pericardial, 112 pericardial, and 5 ventricular signals plotted on alog scale.

FIG. 5 shows the threshold analysis. The number of false positivesplotted against the number of false negatives for a range of differentthreshold values for the algorithm analysis (open circles) and the FFTanalysis (closed circles).

FIG. 6 shows an example of the in vivo data. Algorithm and method outputfor all signals from one animal, including the output for allpericardial signals (open circles) and non-pericardial signals (closedcircles), as well as the presence of the thresholds Ta (solid line) andTb (dashed line), showing the separation of signals.

FIG. 7 shows the threshold values and performance characteristics of thealgorithm compared to the FFT analysis.

FIG. 8 shows an indication of pericardial access. Incoming signals fromthe fiber optic sensor in the access needle during a ventilation hold(to suppress the breathing component of the waveform), as the needle ismoved through the parietal pericardial membrane and into the pericardialspace. An abrupt shift in the frequency characteristics of the pressuresignal becomes apparent upon entry into the pericardium, as a largetemporal signal fluctuating at the frequency of the heart rate appears.

FIG. 9 is an illustration of an exemplary system according to aspects ofthe invention, as used on a subject.

FIG. 10 is a schematic diagram of an exemplary access needle accordingto aspects of the invention.

FIG. 11 is a schematic block diagram for a system or related method ofan embodiment of the present invention in whole or in part.

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the invention is not limited to the particularmethodology, protocols, and configurations, etc., described herein, asthese may vary as the skilled artisan will recognize. It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the invention. It also is be noted that as used herein and inthe appended claims, the singular forms “a,” “an,” and “the” include theplural reference unless the context clearly dictates otherwise. Thus,for example, a reference to “a sensor” is a reference to one or moresensors and equivalents thereof known to those skilled in the art.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which the invention pertains. The embodiments of theinvention and the various features and advantageous details thereof areexplained more fully with reference to the non-limiting embodiments andexamples that are described and/or illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale, and features of one embodiment may be employed with otherembodiments as the skilled artisan would recognize, even if notexplicitly stated herein. Descriptions of well-known components andprocessing techniques may be omitted so as to not unnecessarily obscurethe embodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the invention maybe practiced and to further enable those of skill in the art to practicethe embodiments of the invention. Accordingly, the examples andembodiments herein should not be construed as limiting the scope of theinvention, which is defined solely by the appended claims and applicablelaw. Moreover, it is noted that like reference numerals referencesimilar parts throughout the several views of the drawings.

Although various embodiments may be described in the context of asubxiphoid access, and epicardial treatment, for clarity, the inventionencompasses and may be applied to other types of treatment, particularlythose taking place in, proximate to, and/or or penetrating tissue ororgans of the body including different pressure frequencycharacteristics.

An aspect of an embodiment of the present invention system (and relatedmethod) includes a precision fiber-optic pressure sensor and a novelsignal analysis algorithm, method, technique and system for identifyingpressure-frequency signatures which, in the clinical setting, may allowfor safer access to, for example, the pericardial space.

As discussed further below, aspects of the invention includeinstrumentation constituting the improved subxiphoid access system, aswell as the structure of the data analysis algorithm, method, techniqueand system. Test results of the use of such systems and methods are alsoprovided based on a series of institutionally approved in vivo trials ofthe intra-thoracic navigation of the tip of a pressure-frequency sensingTuohy needle in adult canines. The inventors have further assessed theability to limit the number of residual false positive and falsenegative identifications of needle location within the pericardium, ascompared with the empirical method as employed in the trials by apracticing electrophysiologist.

Instrumentation

A series of ACUC approved animal trials were performed in the Universityof Virginia vivarium by a practicing electrophysiologist on ten canines(>22 kg), using the standard-of-care pericardial access techniquescurrently employed in the clinical Electrophysiology Lab. Anesthesia wasinduced using fentanyl and etomidate, and maintained with isoflurane.Canines were mechanically ventilated at a constant rate for the durationof the trials, between 13 and 16 breaths per minute. For each animal, aminimum of 4 pericardial access procedures were performed with astandard 17 gauge epidural (Tuohy) needle. The clinician guided it tothe pericardium by fluoroscopy and injection of contrast agent. Inselected procedures the final pericardial location was verified byplacing a guide wire through the access needle's lumen and observing itslocation under fluoroscopy. Hydrodynamic pressure data from the accessneedle (>10 s records) were acquired during each procedure at locationsintra-thoracic prior to the diaphragm, intra-thoracic after puncturingthe diaphragm, and intra-pericardial. The location of the needle, andtherefore our determination of each signal's pericardial ornon-pericardial nature, was identified by the clinician's judgment. Someof the data were taken with the needle held in static positions, and therest while it was being moved from the thoracic cavity into thepericardium, as well as upon withdrawal. Certain pressure recordingswere made with ventilation held to anatomically remove breathing signalsfrom the waveform.

During the access procedures, four simultaneous measurements wereacquired on a laboratory computer using LabVIEW SignalExpress™ (NationalInstruments, Austin, Tex.). The four measurements included the pressureas monitored by the sensor in the needle's tip, the left ventricle (LV)pressure, the right femoral artery (A-line) pressure, and theelectrocardiogram (ECG) voltages.

In an initial study of pericardial pressure dynamics, a strain gauge onthe proximal end of the access needle was used to sense the pressures atthe distal tip via a column of fluid between it. Although suchinstrumentation is highly effective when utilized properly for readingstatic pressure measurements from a single location, it is difficult toemploy for reading small-amplitude hydrodynamic pressures when thefluid-filled conduit (be it a sheath, catheter, or needle) is moving.This is because the fluid filled column has weight, and hence thefluid's hydrostatic pressure contributes inertial artifacts to theamplitude of the pressure read at the proximal end of the fluid conduit.If the needle's orientation relative to gravity is not maintainedunchanged while it is being advanced towards the pericardium, theresulting fluctuations in the force transduced by the strain gaugeintroduce substantial noise onto the signal. This makes the techniquevery difficult to employ in the clinical setting during an accessprocedure.

Therefore, a more viable method of monitoring pressures at the tip of adynamically shifting access needle is desired. In embodiments, exemplarysystems may include a solid-state, or optical, pressure sensor. As usedherein, “pressure sensors” may preferably include sensors that arecapable of registering not only steady-state pressure, but also pressurefrequency over time, which may require rapid responsiveness andaccuracy. In embodiments, such sensors may also be understood asincluding, and/or in communication with, a computer processor configuredto determine pressure frequency from pressure signals. Varying pressureinformation received over a period of time may also be referred togenerally as pressure frequency information.

A fully solid-state sensor was implemented by the inventors including afiber optic (Fabry-Perot resonator) pressure transducer (FISO, modelFOP-MIV-BA-C1-F2-M2-R1-SC, Quebec, Canada), and was introduced into thelumen of an access needle, with the transducer tip placed just withinthe edge of the distal tip of the needle so that it did not protrudeinto the tissue. The sensor at the distal tip of the fiber had adiameter of 550 μm. This was followed by a 20-mm segment of bare fiberof roughly half the sensor's diameter, with the remaining length encasedin a PTFE sheath all the way to the connector at the proximal end. Theresolution was ≈0.3 mm Hg, with a residual thermal drift of <−0.05% °C.⁻¹. In embodiments, a pressure sensor, such as an optical sensor, maybe affixed to, or proximate to, an end of an access needle. As discussedfurther below, securing the pressure sensor may be advantageous inreducing unwanted noise, but is not necessarily required.

The optical fiber itself was fixed in place at the proximal end of theneedle by passing it through a Tuohy-Borst adapter which was coupledonto the needle's Luer lock. In this instance, the transducer was notfixed at the tip of the needle, since it had to be removed from theinner lumen so that a guide wire could be passed through the needle toverify the location inside the pericardium. This was accomplished bydecoupling the Tuohy-Borst fitting from the needle's Luer lock andwithdrawing the sensor. During use, the fiber optic cable was connectedto its mating light source/signal conditioning device (FISO, modelEVO/FPI-HR, Quebec, Canada). The voltages from the analog output boardon the signal conditioner were read by an analog-to-digital dataconverter (National Instruments, model USB-6009, Austin, Tex.) andstored for subsequent analysis.

As mentioned above, three standard measures of cardiac dynamics wereacquired in synchrony with the needle pressures during each trial.First, the LV pressures were monitored via a clinical pigtail catheter,which was inserted into the left ventricle from the animal's carotidartery. The pigtail catheter was flushed and filled with saline, and thepressure in it was monitored by a clinical flush-through transducer(Hospira, model Transpac™, Lake Forest, Ill.). Second, central A-linepressures were obtained via a 10 French sheath, placed in the femoralartery of the canine. The sheath was flushed and filled with saline, andmonitored by a transducer identical to that used in the LV pigtailcatheter. Both the LV and A-line transducers were connected to a dataacquisition and signal conditioning board (National Instruments, modelUSB-9237, Austin, Tex.) via a custom-built cable that bridged the RJ11jack of the transducer wiring to the RJ50 input plug on the board. Theseresulting data were useful in assessing the effect of cardiac dynamicson pericardial pressures.

Third, electrophysiological data were taken during the procedures. Thebipolar electrical signal between leads on the right arm (RA) and leftarm (LA) was monitored by a custom-built ECG reading system. The ionicpotentials were transduced to electronic potentials via standardclinical pediatric ECG electrodes (Ambu®, model Blue Sensor M, GlenBurnie, Md.). The RA and LA leads were connected to a custom-built,differential-amplifier signal conditioning circuit (Burr-Brown/TI modelOPA2227 P operational amplifiers, Dallas, Tex.) to buffer, amplify, andbandpass-filter the incoming signal. The output signal from the circuitwas connected to the second port of the A/D data acquisition device. Thesignals from both data acquisition units were transferred to thelaboratory computer via USB 2.0 connections at a rate of ˜1.6 kHz by theLabVIEW SignalExpress™ software.

Data Processing

Fast Fourier Transform Analysis

For each canine, a set of non-pericardial (pre-diaphragm andpost-diaphragm thoracic signals) and intra-pericardial signals werecollected. These signals were examined for segments with minimal noise,and suitable samples 10 s long were extracted for further analysis. Ahanning window was applied to the segment, and a linear-peak FastFourier Transform (FFT) was carried out in LabVIEW. Using the embeddedvirtual instrument functions on the same 10 s segment of any of thecardiodynamic reference signals, the average heartbeat frequency forthat segment was calculated, and the magnitude of the FFT at thatspecific frequency point was identified as the signal magnitude ofinterest at the heart rate. Altogether, 98 non-pericardial and 112pericardial signals were collected and analyzed in this manner.

Following the collection of signal-magnitude data from all 210 signals,an automated search was performed to determine how well a thresholdvalue of the cardiac signal strength at the heart-rate frequency couldseparate pericardial from non-pericardial locations of the needle tip. Acustom program in MATLAB® was written and used to numerically evaluatethe magnitude data. The frequency component at the heart rate issignificantly less in the non-pericardial signal when compared to thepericardial signal. The goal then was to define a threshold pressurewhich indicated the best obtainable separation between non-pericardialand pericardial signals by inferring the presence of false positives andfalse negatives (i.e., non-pericardial signals above the threshold,denoted by false_(p); pericardial signals below the threshold, denotedby false_(n), respectively). Possible threshold values were tested fromthe range of 0 to 0.6 mmHg (0 to 80 Pa), in increments of 0.0001 mmHg(0.013 Pa). For each possible threshold value within that range, thenumber of non-pericardial signal magnitudes above that threshold (falsepositives) and the number of pericardial signal magnitudes below thatthreshold (false negatives) were counted. The best obtainable thresholdwas then found by minimizing the scoreScore=W _(p)·false_(p) +W _(n)·false_(n)  (1)where the scoring weights W_(p) and W_(n) indicated the relativeimportance of false positives and false negatives. In a givencalculation for best obtainable threshold, W_(p) and W_(n) remainconstant. A best obtainable threshold was found for every combination ofvalues of W_(p) and W_(n) ranging from 0.1 to 1.0 in increments of 0.1.The nature and application of the findings is discussed below in theResults Section.

Custom Algorithm and Method Analysis

Additional investigations were conducted for determining if a cardiacsignal was present in the needle-tip signal, taking into account theinconsistency of the heart rate in many of the experiments and, ingeneral, the spectral complexity of the heartbeat signal. For example,heart-rate variability could not only cause FFT spectral leakage, buteven separate the FFT cardiac peak into distinct sub-peaks of lowermagnitude, making FFT-based measurements inconsistent. Using the ECG asa reference signal, the needle sensor's waveform was segmented betweenconsecutive R waves in the QRS complex of the signal. Acustom-synthesized algorithm that combined aspects of phase sensitivedetection (PSD) and matched filtering then analyzed it to ascertain thepresence of a consistent waveform with a fundamental frequency at thatof the heart rate, but with the ability to accommodate beat-to-beatvariations in heart rate. A flow chart for this algorithm is shown inFIG. 1.

In FIG. 1, two parallel paths denote the analysis of the referencewaveform (left) and the input needle waveform (right). Boxes are labeledas either a signal processing step (white background) or a waveform(shaded background). The functions of the blocks/elements in FIG. 1 areexplained in detail below, and FIGS. 2 and 3 show the nature of theoperation of the algorithm as the data stream progresses through theblocks/elements of FIG. 1.

For the algorithm and method analysis, the same signals from the FFTanalysis were used for the algorithm and method analysis, and anautomated program in LabVIEW performed it on each of the needle sensor'swaveforms. After reviewing the spectral structure of all the types ofwaveforms that were captured, none of which contained signal components≧100 Hz (which was taken to be the Nyquist frequency), the signals weredown-sampled to 2×100 Hz=200 Hz to allow for more precise filtering. Allfiltering routines were performed in a zero-phase implementation,infinite impulse response (IIR) mode, which filtered the forward signaland then reversed and refiltered it, and reversed it again in order toremove all phase-sensitive filtering transients. Moreover, all of thesimple high- and low-pass filters were of elliptic structure in order tominimize the order of the filter, thus both minimizing start- andend-signal transients and maximizing the computational efficiency.

Reference Waveform Segmentation

The ECG waveform served as the reference for the algorithm and method inidentifying the timing of cardiac cycles in the animal. The ECG signalsegment was notch-filtered at 60 Hz (Q≈50) to eliminate any residualpower-line noise that the signal conditioner did not fully remove. Thesignal was then high pass-filtered at a cutoff frequency of 20 Hz, tomaintain only the high frequency elements that compose the QRS complex.Then, the strength of the remaining high-frequency noise components wereattenuated with an undecimated wavelet transform using a biorthogonal4_4 (FBI) wavelet to insure that only the QRS peak of interest remained.To provide for consistency in subsequent mathematical steps, the signalterms were then rectified by their absolute value and the remainingdetectable but extraneous peaks were smoothed with a moving averagefilter. As shown in FIG. 2, the surviving peaks were then identified asthe R complex or the center of the QRS complex in the cardiac cycles, inorder to segment the waveform into heartbeats according to theelectrophysiology of the patient.

FIG. 2 shows the ECG waveform segmentation. An example ECG waveform(top, solid line) is shown, as well as the resulting segmentation pointsat the R wave (top, dotted line). The processed ECG according to thealgorithm, method, and technique in FIG. 1 is shown as well (bottom).

Analysis of the Pressure Waveform Produced by the Needle's Sensor

The 10 s records of the needle's hydrodynamic pressure signal werehigh-pass filtered with a cutoff frequency of 1 Hz to attenuate lowfrequency breathing components. The resulting signal was furtherseparated into cardiac segments according to the timing points foundusing the ECG analysis above. Only cardiac segments containing a fullcardiac cycle (a start and an end point) were analyzed. A goal of thealgorithm and method was to quantitatively compare the waveform betweenconsecutive cardiac segments. In many implementations of phase-sensitivedetection, the input waveform is multiplied by a reference signal inorder to evaluate whether the waveform is of the desired frequency andphase. If the input waveform's characteristics match those of thereference waveform, then the multiplied signal will be perfectlyrectified. For reasons discussed below, in place of a common referencewaveform which would be used for that multiplication, the algorithminstead used an interpolated version of the previous cardiac segment asthe reference waveform for the currently analyzed cardiac segment.Examples of both pericardial and non-pericardial signals are shown inFIG. 3.

FIG. 3 shows the algorithm and method signal analysis. Pericardial(left) and non-pericardial (right) examples of the analysis of cardiacsignal segments. Current cardiac segment (G), previous cardiac segmentinterpolated and normalized (B), and multiplied signals prior tointegration (R). Prior to that multiplication, the previous cardiacsegment was normalized to fit between ±1 to insure uniformity ofreference scale size. Then, the area under the resulting signal segmentwas integrated to arrive at an exact measure of the level of signalrectification. A high positive output of the integration step correlatedto a significant signal with a fundamental frequency at the heart rate,while other signals integrated towards zero. Because of the timedependency of the integration process, the integrated output was thenmultiplied by the fundamental frequency of that segment fornormalization in the time domain. A signal which is of higher frequencywill have a shorter integration time, and this is why the integration isnormalized by the frequency of the segment. The outputs for each cardiacsegment were then averaged over the 10 s signal window. Algorithmthresholds were found using the same scoring function as that employedfor the FFT data as described above.

This routine combines features of both match filtering and PSD. If themain signal component which is present is fundamentally matched tocardiac dynamics, then the signal should repeat between cardiacsegments, regardless of noise. It is assumed that if the needle is inthe pericardial space, then there should be good agreement between thecurrent and last cardiac segment of the waveform. However, instead ofconvolving the signals or performing Fourier multiplication of thesignals, which is computationally inefficient or requires a large windowof consistent repeatable signal, respectively, the signal may beintegrated.

Another significant point is that when integrating a high-noise signal,as more time points are integrated, the integral of white noise tends tozero. Hence, this algorithm and method also functions efficiently inhigh noise scenarios. In summary, this approach, which employs the ECGas the reference waveform, is a more elaborate but robust way ofascertaining the presence and magnitude of a cardiac signal pattern inthe needle sensor's pressure signal, which can take into account andadjust for irregular or inconsistent heart rates.

Results

Average Signal Output

The signal magnitude at the heart rate frequency of the FFT of the 98non-pericardial waveforms was (0.09±0.08) mmHg, and it was (0.55±0.31)mmHg for the 112 pericardial signals. Unpaired, one-tailed t-testsrevealed a statistically significant difference in means of the twogroups (p<0.01). Purposeful ventricular perforation was successful in 5animals, and the mean signal at the heart rate from these 5 measurementswas (24.98±9.34) mmHg, which was significantly greater than themagnitudes for both the non-pericardial and pericardial groups (p<0.01).

The average, dimensionless signal output from the algorithm for the 98non-pericardial waveforms was (0.024±0.03), and (0.21±0.14) for the 112pericardial signals. Average signal output for ventricular signals was(14.74±5.97). As shown in FIG. 4, all groups are significantly differentfrom each other (p<0.01).

Threshold Signal Separation

Using Eq. (1) on both the FFT and algorithm data, a number of thresholdswere found which separated the pericardial from the non-pericardialdata. However, this analysis also revealed some overlap ofnon-pericardial and pericardial signals, i.e., regions of non-separationof the signals (transition zone in FIG. 7). These overlaps in signalstrength may have been due to tissue clogs in the needle lumen,imperfect localization of the sensor in or outside of the pericardium,or the presence of a small cardiac signal directly outside thepericardium. The latter-most option is the most likely, especially ifthe needle is being pushed against the pericardial surface, andtherefore is in immediate proximity of the heart. However, this range ofsignal overlap is important, and suggests a need for three separationthresholds of cardiac signal strength for the pericardial accessprocedure in the clinical setting. These three thresholds would providefor the clinically relevant separation of four regimes ofpressure-frequency signal dynamics: (i) away from the pericardium, (ii)very close to the pericardium (the “transition” zone), (iii) safelyinside the pericardium, and (iv) dangerously within the ventriculartissue. Moving from the thorax towards the heart, the first threshold,T_(a), identifies the beginning of the transition zone, where a smallcardiac signal first arises. The second threshold, T_(b), identifies thebeginning of the pericardial zone, where the signal structure isdefinitively pericardial. The third threshold, T_(c), would indicatethat there has been perforation of the ventricle, which would beassociated with a vast increase in cardiac signal strength.

After analyzing both the FFT and algorithm data and method, the valuesfor thresholds T_(a) and T_(b) were selected. The number of associatedfalse positives and false negatives are displayed in FIG. 7.

FIG. 7 shows the threshold values and performance characteristics of anexemplary algorithm compared to the FFT analysis. The exemplaryalgorithm and method is shown to be more efficient at separatingpericardial from non-pericardial signals, as indicated by the decreasednumber of signals in the transition zone between T_(a) and T_(b), aswell as the increase in the number of signals which fall above or belowthe appropriate threshold.

The separation of non-pericardial from pericardial signals is the mainfocus in what follows. This is because the separation of ventricularfrom non-ventricular signals is easily achieved for T_(c) without anyfalse outputs. The performance of both the FFT and algorithm analyses(and related methods) of the data is shown in FIG. 5, which shows theirrelative abilities to limit both false positives and false negativesover a range of threshold values.

False positives are more of a procedural nuisance than a safety concern.On the other hand, false negatives are dangerous, because the clinicianmight continue to advance the access needle into the ventricle if theneedle is actually pericardial but the algorithm indicated that it wasinstead non-pericardial. Therefore, one object of the invention is tonot only minimize the total number of false outputs (of both kinds), butto make the minimization of false negatives the highest priority. Thecustom-synthesized algorithm is able to minimize the number of falsenegatives with much fewer false positives (see FIG. 5), making it a moreeffective tool than FFT analysis for clinical assessment of needlelocation using pressure-frequency guidance. See Table I forrepresentative values of T_(a) and T_(b), and see FIG. 6 for a plot ofthe signal outputs found for one of the animals.

The resulting threshold values in the algorithm are 0.0405 for T_(a).0.077 for T_(b), and 4 for T_(c). Of the 210 non-ventricular pressuremeasurements, 87.14% of the acquired signals fell in the appropriatezone upon analysis with the algorithm, with 1.43% of the signalsidentified as false negatives, 1.90% of the signals identified as falsepositives, and 9.52% of the signals in the transition zone between T_(a)and T_(b). All 5 (100%) ventricular measurements fell above T_(c), withno false negatives or false positives regarding signals falling on thewrong side of T_(c).

It is important to address the pericardial signal outputs which fallbeneath both T_(a) and T_(b) (i.e., the false negatives shown in FIG.7). Using an exemplary algorithm and method, one of the false negativesfrom the FFT analysis was remedied, because the algorithm was able totake into account the complexity of the pericardial signal, while theFFT approach could not. While there were still three false negativesassigned by the algorithm, the inventors found that all were caused bythe presence of a large number of pre-ventricular contraction (PVC)beats. Although the algorithms and methods used in this case wereefficient at handling solitary PVC beats in a given window, in each ofthe three instances of false negatives the majority of the waveform wascomposed of PVC beats. These beats caused lengthy inconsistencies in thecardiac dynamics, making all of the pressure-signal dynamicsinconsistent as well. In all three instances of false negatives for thealgorithm, the time before the signal is PVC-free, and the signal outputoccurs above T_(b) in the appropriate signal zone. This proved thatthese signals were anatomically pericardial, but that the inconsistentcardiac dynamics caused by the PVCs were impossible to track.

Thus, it was noted that it is possible that solitary PVC beats may causean error in the algorithm and method if only one previous beat is usedfor comparison to the current cardiac segment. In embodiments, sucherrors may be avoided, for example, by adapting the algorithm tocompare, for example, the previous two to five beat segments. There areseveral ways in which it might be accomplished, e.g. by acquiring andaveraging the parameters of two neighboring PVC beats and using thatresult to drive the segmentation of the needle waveform. Other criteriamay be applied to disregard a reference phase. Such criteria may rely,for example, on an appropriate statistical measure used to identify asignificantly irregular beat pattern (e.g., a sudden change in thefrequency band in which the beat occurred, indicating the occurrence ofwhat in nonlinear dynamics is called a “transition to chaos”).

In embodiments, the algorithm may be adapted to focus primarily oncapturing the first cardiac segment once the needle is positionedpericardially. If one PVC beat were to occur at that first segment, thenthe algorithm would simply have a delayed response of one extra cardiacsegment, and the probability of a PVC occurring at such a preciselydefined moment is very low.

Pericardial access can be critical for curing several cardiac conditionsbut it is fraught with a high risk of both procedural failure andventricular perforation. To address these issues, the inventors measuredthe pressure-frequency signals generated by a solid state (fiber optic)sensor at the tip of a pericardial access needle, and collected ECGsignals in synchrony. By employing a novel algorithm, method, techniqueand system that contains characteristics of both matched filtering andphase-sensitive detection to process those data, the location of theneedle's tip was distinguished accurately. In analogy with phasesensitive detection, the present subject matter uses measures of cardiacdynamics to separate the incoming needle's signal into distinctsections. Also, just as matched filtering checks an incoming signalaccording to a known outgoing signal, exemplary algorithms according toaspects of the invention may be configured to compare the currentcardiac section of the signal to the previous section, to search for asimilar pattern. Such algorithms, and associated methods, techniques andsystems, can distinguish pericardial from non-pericardial waveformsregardless of signal dynamics and structure, as long as a signal withthe fundamental frequency (equal to the cardiac frequency) is present atany given time. This is significant, because as different parts of thepericardium are accessed at different needle insertion angles, thesignal structure can change.

It was found that the exemplary algorithms, and associated methods,techniques and systems, presented herein provided a better approach thantracking an FFT peak for several reasons. First, FFT peaks take time toestablish in a signal window, since they sample global (and not local)frequency content. However, use of an exemplary algorithm in systemssuch as those described is expected to decrease the time lag needed toestablishing the needle's presence in the pericardium to just onecardiac cycle (i.e., ˜1 s).

In order to achieve such results, it is expected that a sensor fixed, orlocked, proximate to the end of the needle would be advantageous. Thatis, configurations in which the fiber optic sensor is left un-fixedwithin the tip of the needle (e.g. so that it can be easily extractedwhenever a guide wire had to be passed into the needle's lumen), mayresult in some mechanical noise being imposed on the signal based on theresidual motion of the sensor's tip. In order to reduce the overalleffect of such noise, the algorithm's output may also be averaged overan extended window.

Also, as the patient's heart rate undergoes normal shifts, both spectralleakage and separation of FFT peaks is a concern. Since the systems andmethods described herein track the patient's cardiac dynamics directly,embodiments may also provide means of tracking heart rate duringaccelerations into tachycardia, decelerations into bradycardia, andinconsistencies as occur in atrial fibrillation. Also, embodiments ofthe invention may be useful for patients with low cardiac signalstrength in the pericardial waveform because of previous cardiac surgeryand the resulting pericardial adhesions.

Another important aspect of the invention is to quantify the pressurewaveform at the needle's tip as it breaches the pericardial membrane,going from non-pericardial to pericardial anatomy. In studying this, theinventors looked at several examples of dynamic pressure measurementsmade while the needle both breached into the pericardium and was pulledout of it were acquired, and an example is shown in FIG. 8.

FIG. 8 shows an indication of pericardial access. Incoming signals fromthe fiber optic sensor in the access needle during a ventilation hold(to suppress the breathing component of the waveform), as the needle ismoved through the parietal pericardial membrane and into the pericardialspace. The signal transition occurs just before the 8 second mark. It isevident that there is a discrete addition of cardiac signal to thewaveform at the point of entering/leaving the pericardium. However, itis also evident that there is a transition zone, which most likelyoccurs as the needle is right outside the pericardium, which containssmall levels of cardiac signal, justifying the use of T_(a), to warn theclinician they may in fact be close to the pericardium, although notintra-pericardial.

According to aspects of the invention, embodiments may also be adaptedto allow for the analysis to occur in real time. Such adaptation mayinclude, among other features, real-time data analysis during signalacquisition, as opposed to post-processing of data segments. Also, astatistical analysis of this and other pericardial and non-pericardialsignals may be analyzed to determine not clinical thresholds betweenanatomical zones, as well as determining confidence intervals for thosethresholds. This would allow for systems and methods that tell theclinician which anatomical zone they are in with statistical certainty.The needle itself is also an important part of the access system thatcan be improved to provide real-time or near real-time analysis. Thedevice used by the inventors was a Tuohy epidural needle, but with thefiber optic sensor threaded through the lumen to the tip. However, thepressure sensor was neither fixed to the tip of the needle, nor designedto be otherwise housed by the Tuohy needle, and this allowed the fiberoptic tip to move in certain situations, thus increasing noise anddecreasing signal fidelity. A needle with, for example, a fixed orlocked pressure sensor would be expected to produce readings with alarger signal-to-noise ratio.

As discussed above, following in vivo studies on 10 adult canine models,the inventors analyzed 215 pressure-frequency measurements made at thedistal tip of the access needle, of which 98 were from non-pericardial,112 were from pericardial and 5 were from ventricular locations. Theneedle locations as identified by the exemplary systems and methods weresignificantly different from each other (p<0.01), and systems andmethods showed improved performance when compared to a standard FFTanalysis of the same data. Moreover, the structure of the algorithm,method, technique and system can be advantageously used to minimize, orovercome, the time lags intrinsic to FFT analysis, such that theneedle's location may be determined in near-real time.

An advantage accruing from the use of the means and method of theinvention is, but not limited thereto, the ability to allow for pacingof the epicardium itself with relative ease.

FIG. 9 shows a human subject 50 undergoing insertion of an access needle100 into the pericardial region 6 along a desired pathway 5. The accessneedle 100 may include a pressure (or pressure frequency) sensordisposed proximate to a distal end of the needle. Other sensors (notshown) may also be disposed at or in different locations of the subject50, such as, for example ECG sensors, and/or ventricle or arterialpressure sensors. The access needle 100 can also be used to access thethorax 51 of the patient 50. The access can be accomplished by aninterventional procedure, such as a sub-xiphoid puncture, or a surgicalprocedure. It is important during the procedure that critical organs andanatomical structures within that region are not damaged by inadvertentinsertion of the access needle 100 into them during the needle placementprocess. The physiological functions of the internal organs, spaces andstructures of the body within that region occur at different levels ofhydrostatic pressure. For instance, the stomach 2 exerts a positivepressure (P₊) on its bounding structures, including the diaphragm 3.Meanwhile, the lung 1 will function at negative pressures (P⁻) in therange of 5 to 10 atmospheres, with the heart 4 maintaining surfacepressures of approximately 12 mm Hg. Therefore, there are a variety ofpressures (as well as pressure frequencies) that might be sensed by theaccess needle 100 during placement of it.

It should be appreciated that as discussed herein, a subject may be ahuman or any animal. It should be appreciated that an animal may be avariety of any applicable type, including, but not limited thereto,mammal, veterinarian animal, livestock animal or pet type animal, etc.As an example, the animal may be a laboratory animal specificallyselected to have certain characteristics similar to human (e.g. rat,dog, pig, monkey), etc. It should be appreciated that the subject may beany applicable human patient, for example.

In an aspect of an embodiment of the invention, the access needle 100 isused for accessing the thorax 51 and pericardium of a subject 50,wherein the access needle comprises a pressure frequency sensor orsystem for sensing pressure frequency in the thorax, the pericardium orother tissue of the heart. However, it should be appreciated thatvarious embodiments of the present invention device or system and methodare not necessarily limited to accessing the thorax and pericardium of asubject. It may also be used in the organ structures or tubularstructures in the thorax as well as other locations or regions in thebody. An organ includes, for example, a solid organ, a hollow organ,parenchymal tissue (e.g., stomach, brain, esophagus, colon, rectum,kidneys, liver, etc.) and/or stromal tissue. Hollow organ structuresincludes, for example, stomach, esophagus, colon, rectum, and ducts, orthe like. A tubular structure may include a blood vessel. A blood vesselmay include one or more of the following: vein, venule, artery,arterial, or capillary.

FIG. 10 shows a schematic diagram of the details of construction of oneembodiment of said access needle 100. The needle 100 has a distal end300 and a proximal end 7. In some embodiments, the needle 100 will havea length of about 10 to 25 cm and will be of about 14 gauge size, but itcould be smaller or larger as suits the anatomy of the patient and theneeds of the clinician using it. The needle may have markings 8nominally at about 1 cm locations along its axial length. The markingscan be used to observe the depth of insertion of the needle 100 alongthe pathway 5 shown in FIG. 9. At the proximal end 7 of the needle,there can be at least one aperture, such as a plurality of channels 10that provide means for achieving the functionalities of the subjectinvention. These can include a port 11 to which the manometry orpressure frequency sensing apparatus is connected and/or a port 12 intowhich a guidewire, sheath, catheter, puncture needle, or other devicesor tools that may be inserted for passage through and withdrawal from adistal aperture, such as an end port hole 9. The puncture needle (notshown) can be in communication with a spring and used to puncture tissueof a patient. A port 13 can be connected to a multi-channel structure,conduit or connector, such as a three-way stopcock 15, for example, withinlet ports 14 to allow entry and control of the flows of infusionagents or desired fluid or medium. This flow can include providing afluid, liquid, gas, or mixtures thereof, with or without therapeuticagents, drugs or the like, heating and/or cooling of the fluid, chemicalreactions and/or physical interactions between the components of thefluid, and draining of the fluid. At the distal end 300 of said needle100, there can be an aperture, such as a beveled end port hole 9. Saidneedle 100 might serve as the placement mechanism for a sheath orcatheter means 200, only the distal portion of which is shown in FIG.10. In another embodiment, the sheath or catheter means 200 can beplaced inside the needle 100. In one embodiment, the needle could have adivider running the length of its axis, thus creating two or more zones,or lumens, within it. One could be used for pressure frequency sensing,while the other could be used for passage of a guide wire, catheter,sheath, or puncture needle or other device or injection of a contrastagent or other medium. The sensing component of the needle could be muchsmaller in mean diameter than the other component, with the sensingorifice positioned just in front of the other component's orifice (orother locations, positions and sizes as desired or required). As aresult, if the sensing component detected a perforation of the rightventricle, the resultant hole created by the puncture devices or thelike would thus be small. Moreover, the entire distal tip of the innerneedle assembly could also be re-shaped so that it is similar to a Tuohyneedle or some other suitable configuration, thus further minimizing therisk of inadvertent perforations.

Turning to FIG. 11, FIG. 11 is a functional block diagram for a computersystem 900 for implementation of an exemplary embodiment or portion ofan embodiment of present invention. For example, a method or system ofan embodiment of the present invention may be implemented usinghardware, software or a combination thereof and may be implemented inone or more computer systems or other processing systems, such aspersonal digit assistants (PDAs) equipped with adequate memory andprocessing capabilities. In an example embodiment, the invention wasimplemented in software running on a general purpose computer 90 asillustrated in FIG. 11. The computer system 900 may includes one or moreprocessors, such as processor 904. The Processor 904 is connected to acommunication infrastructure 906 (e.g., a communications bus, cross-overbar, or network). The computer system 900 may include a displayinterface 902 that forwards graphics, text, and/or other data from thecommunication infrastructure 906 (or from a frame buffer not shown) fordisplay on the display unit 930. For example, information indicating aninferred location of an access needle, warnings related to an inferredlocation, etc. Display unit 930 may be digital and/or analog.

The computer system 900 may also include a main memory 908, preferablyrandom access memory (RAM), and may also include a secondary memory 910.The secondary memory 910 may include, for example, a hard disk drive 912and/or a removable storage drive 914, representing a floppy disk drive,a magnetic tape drive, an optical disk drive, a flash memory, etc. Theremovable storage drive 914 reads from and/or writes to a removablestorage unit 918 in a well known manner. Removable storage unit 918,represents a floppy disk, magnetic tape, optical disk, etc. which isread by and written to by removable storage drive 914. As will beappreciated, the removable storage unit 918 includes a computer usablestorage medium having stored therein computer software and/or data.

In alternative embodiments, secondary memory 910 may include other meansfor allowing computer programs or other instructions to be loaded intocomputer system 900. Such means may include, for example, a removablestorage unit 922 and an interface 920. Examples of such removablestorage units/interfaces include a program cartridge and cartridgeinterface (such as that found in video game devices), a removable memorychip (such as a ROM, PROM, EPROM or EEPROM) and associated socket, andother removable storage units 922 and interfaces 920 which allowsoftware and data to be transferred from the removable storage unit 922to computer system 900.

The computer system 900 may also include a communications interface 924.Communications interface 124 allows software and data to be transferredbetween computer system 900 and external devices, including, forexample, pressure sensors as described herein, ECGs, etc. Thecommunications interface 924 may include a plurality of physical and/orvirtual input/output ports configured to communicate with differentsensors, etc. Examples of communications interface 924 may include amodem, a network interface (such as an Ethernet card), a communicationsport (e.g., serial or parallel, etc.), a PCMCIA slot and card, a modem,wifi, Bluetooth, etc. Software and data transferred via communicationsinterface 924 are in the form of signals 928 which may be electronic,electromagnetic, optical or other signals capable of being received bycommunications interface 924. Signals 928 are provided to communicationsinterface 924 via a communications path (i.e., channel) 926. Channel 926(or any other communication means or channel disclosed herein) carriessignals 928 and may be implemented using wire or cable, fiber optics,blue tooth, a phone line, a cellular phone link, an RF link, an infraredlink, wireless link or connection and other communications channels.

In this document, the terms “computer program medium” and “computerusable medium” are used to generally refer to media or medium such asvarious software, firmware, disks, drives, removable storage drive 914,a hard disk installed in hard disk drive 912, and signals 928. Thesecomputer program products (“computer program medium” and “computerusable medium”) are means for providing software to computer system 900.The computer program product may comprise a computer useable mediumhaving computer program logic thereon. The invention includes suchcomputer program products. The “computer program product” and “computeruseable medium” may be any computer readable medium having computerlogic thereon.

Computer programs (also called computer control logic or computerprogram logic) are may be stored in main memory 908 and/or secondarymemory 910. Computer programs may also be received via communicationsinterface 924. Such computer programs, when executed, enable computersystem 900 to perform the features of the present invention as discussedherein. In particular, the computer programs, when executed, enableprocessor 904 to perform the functions of the present invention.Accordingly, such computer programs represent controllers of computersystem 900.

In an embodiment where the invention is implemented using software, thesoftware may be stored in a computer program product and loaded intocomputer system 900 using removable storage drive 914, hard drive 912 orcommunications interface 924. The control logic (software or computerprogram logic), when executed by the processor 904, causes the processor904 to perform the functions of the invention as described herein.

In another embodiment, the invention is implemented primarily inhardware using, for example, hardware components such as applicationspecific integrated circuits (ASICs). Implementation of the hardwarestate machine to perform the functions described herein will be apparentto persons skilled in the relevant art(s).

In yet another embodiment, the invention is implemented using acombination of both hardware and software.

In an example software embodiment of the invention, the methodsdescribed above may be implemented in SPSS control language or C++programming language, but could be implemented in other variousprograms, computer simulation and computer-aided design, computersimulation environment, MATLAB, or any other software platform orprogram, windows interface or operating system (or other operatingsystem) or other programs known or available to those skilled in theart.

The description given above is merely illustrative and is not meant tobe an exhaustive list of all possible embodiments, applications ormodifications of the invention. Thus, various modifications andvariations of the described methods and systems of the invention will beapparent to those skilled in the art without departing from the scopeand spirit of the invention. Although the invention has been describedin connection with specific embodiments, it should be understood thatthe invention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled in thememory circuit design, memory circuit manufacture or related fields areintended to be within the scope of the appended claims.

The following patents, applications and publications as listed below andthroughout this document are hereby incorporated by reference in theirentirety herein.

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PCT International Application Serial No. PCT/US2010/033189, filed Apr.30, 2010, entitled “Access Trocar and Related Method Thereof”.

PCT International Application Serial No. PCT/US2008/082835, filed Nov.7, 2008, entitled, “Steerable Epicardial Pacing Catheter System PlacedVia the Subxiphoid Process,” and corresponding U.S. patent applicationSer. No. 12/741,710 filed May 6, 2010.

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REFERENCES CITED

The following patents, applications and publications as listed below andthroughout this document are hereby incorporated by reference in theirentirety herein.

FOREIGN PATENT DOCUMENTS

-   WO95/10319, Fleischman, et al., “Electrodes for Creating Lesions in    Body Tissue”, April 1995.-   EP 1 129 681 A1, Pezzola, A., “Phacoemulsification Tip”, September    2001.

OTHER PUBLICATIONS

-   J. Tucker-Schwartz et al., “Improved Pressure-Frequency Sensing    Subxiphoid Pericardial Access System: Performance Characteristics    During In Vivo testing,” IEEE Transactions on Biomedical    Engineering, Vol. 58, pp. 845-852 (April 2011).-   J. Tucker-Schwartz et al., “Pressure-Frequency Sensing Subxiphoid    Access System for Use in Percutaneous Cardiac Electrophysiology:    Prototype Design and Pilot Study Results,” IEEE Transactions on    Biomedical Engineering, Vol. 56, pp. 1160-1168 (May 2009).-   F. Sacher, P. Maury, I. Nault, M. Wright, N. Lellouche, N.    Derval, S. Ploux, M. Hocini, P. Bordachar, A. Deplagne, P.    Ritter, J. Clementy, M. Haissaguerre, and P. Jais, “Prevalence of    epicardial scar in patients referred for ventricular tachycardia    ablation,” Heart Rhythm, vol. 6, pp. S175-6, 2009.-   C. Grimard, J. Lacotte, F. Hidden-Lucet, G. Duthoit, Y. Gallais,    and R. Frank, “Percutaneous epicardial radiofrequency ablation of    ventricular arrhythmias after failure of endocardial epproach: a    9-year experience,” J. Cardiovasc. Electrophysiol., vol. 21, no. 1,    pp. 56-61, 2010.-   E. Aliot, W. Stevenson, J. Almendral-Garrote, F. Bogun, C.    Calkins, E. Delacretaz, P. Bella, G. Hindricks, P. Jais, M.    Josephson, J. Kautzner, G. Kay, K. Kuck, B. Lerman, F.    Marchlinski, V. Reddy, M. Schalij, R. Schilling, L. Soejima, and D.    Wilber, “EHRA/HRS expert consensus on catheter albation of    ventricular arrhythmias,” Europace, vol. 11, no. 6, pp. 771-817,    2009.-   E. Sosa, M. Scanavacca, A. d'Avila, and F. Pilleggi, “A new    technique to perform epicardial mapping in the electrophysiology    laboratory,” J. Cardiovasc. Electrophysiol., vol. 7, no. 6, pp.    531-6, 1996.-   E. Sosa, M. Scanavacca, A. d'Avila, J. Piccioni, O. Sanchez, J.    Velarde, M. Silva, and B. Reolao, “Endocardial and epicardial    ablation guided by nonsurgical transthoracic epicardial mapping to    treat recurrent ventricular tachycardia,” J. Cardiovasc.    Electrophysiol., vol. 9, no. 3, pp. 229-39, 1998.-   E. Sosa, M. Scanavacca, A. d'Avila, F. Oliviera, and J. Ramires,    “Nonsurgical transthoracic epicardial catheter ablation to treat    recurrent ventricular tachycardia occurring late after myocardial    infarction,” J. Am. Coll. Cardiol., vol. 35, no. 6, pp. 1442-9,    2000.-   E. Sosa and M. Scanavacca, “Epicardial mapping and ablation    techniques to control ventricular tachycardia,” J. Cardiovasc.    Electrophysiol., vol. 16, no. 4, pp. 449-52, 2005.-   U. Tedrow and W. Stevenson, “Strategies for epicardial mapping and    ablation of ventricular tachycardia,” J. Cardiovasc.    Electrophysiol., vol. 20, no. 6, pp. 710-3, 2009.-   S. Mahapatra, J. Tucker-Schwartz, D. Wiggins, G. Gillies, P.    Mason, G. McDaniel, D. Lapar, C. Stemland, E. Sosa, J. Ferguson, T.    Bunch, G. Ailawadi, and M. Scanavacca, “Pressure frequency    characteristics of the pericardial space and thorax during    subxiphoid access for epicardial ventricular tachycardia ablation,”    Heart Rhythm, vol. 7, no. 5, pp. 604-9, 2010.

The disclosures of all references and publications cited above areexpressly incorporated by reference in their entireties to the sameextent as if each were incorporated by reference individually.

What is claimed is:
 1. A method of inferring the location of a needle ina subject, the method comprising: inserting a needle including a firstsensor into a body of a subject; receiving cardiac waveform informationof the subject from a second sensor; receiving pressure frequencyinformation from the first sensor; segmenting the pressure frequencyinformation based at least in part on the cardiac waveform information;processing the segmented pressure frequency information using analgorithm to obtain algorithm results; and distinguishing, by a computerprocessor, a current location of the needle from another location basedon comparing the algorithm results to a plurality of predeterminedthreshold values.
 2. The method of claim 1, further comprising:determining a reference phase based on the cardiac waveform information;determining a test phase based on the pressure frequency information,wherein, said distinguishing is based on the pressure frequencyinformation from the test phase and the cardiac waveform informationfrom the reference phase.
 3. The method of claim 2, wherein thereference phase is a cardiac phase of the subject immediately precedingthe test phase.
 4. The method of claim 1, wherein at least one of saidsegmenting and processing includes phase sensitive detection and matchedfiltering.
 5. The method of claim 1, wherein processing the segmentedpressure frequency information includes integrating the pressurefrequency information.
 6. The method of claim 1, wherein the cardiacwaveform information includes information derived from a plurality ofcardiac phases of the subject.
 7. The method of claim 1, wherein thecardiac waveform information includes at least one of ventriclepressure, arterial pressure, and electrocardiogram (ECG) signals.
 8. Themethod of claim 1, wherein the current location is a non-pericardiallocation and the other location is a pericardial location, orvice-versa.
 9. The method of claim 1, wherein at least one of thecurrent location and the other location is a thorax of the subject. 10.The method of claim 1, wherein the method includes distinguishingbetween a location remote from the pericardium, a location close to orin contact with the pericardium, and a location inside the pericardium.11. The method of claim 1, wherein the method includes identifying alocation within ventricular tissue of the subject or inside the interiorof the heart of the subject.
 12. A system for accessing one or morelocations of a subject, said system comprising: a needle having a distalend and a proximal end; and a first sensor in communication with saidneedle for sensing pressure frequency in the one or more locations ofthe subject; and a processor configured to: receive cardiac waveforminformation of the subject from a second sensor; receive pressurefrequency information from the first sensor; segment the pressurefrequency information based at least in part on the cardiac waveforminformation; process the segmented pressure frequency information usingan algorithm to obtain an algorithm results; and distinguish a currentlocation of the needle from another location based on comparing thealgorithm results to a plurality of predetermined threshold values. 13.The system of claim 12, wherein the processor is further configured to:determine a reference phase based on the cardiac waveform information;and determine a test phase based on the pressure frequency information,wherein, said distinguishing is based on the pressure frequencyinformation from the test phase and the cardiac waveform informationfrom the reference phase.
 14. The system of claim 13, wherein thereference phase is a cardiac phase of the subject immediately precedingthe test phase.
 15. The system of claim 12, wherein at least one of saidsegmenting and processing includes phase sensitive detection and matchedfiltering.
 16. The system of claim 12, wherein processing the segmentedpressure frequency information includes integrating the pressurefrequency information.
 17. The system of claim 12, wherein the cardiacwaveform information includes information derived from a plurality ofcardiac phases of the subject.
 18. The system of claim 12, wherein thecardiac waveform information includes at least one of ventriclepressure, arterial pressure, and electrocardiogram (ECG) voltages. 19.The system of claim 12, wherein the current location is anon-pericardial location and the other location is a pericardiallocation, or vice-versa.
 20. The system of claim 12, wherein at leastone of the current location and the other location is a thorax of thesubject.
 21. The system of claim 12, wherein the first sensor islockable.
 22. A device for inferring the location of a needle in asubject, said device comprising: a needle including a first sensor; afirst input configured to receive pressure frequency information fromthe first sensor disposed on the needle; a second input configured toreceive cardiac waveform information of the subject from a secondsensor; and a processor configured to: receive cardiac waveforminformation of the subject from the second sensor; receive pressurefrequency information from the first sensor; segment the pressurefrequency information based at least in part on the cardiac waveforminformation; process the segmented pressure frequency information usingan algorithm to obtain an algorithm results; and distinguish a currentlocation of the needle from another location based on comparing thealgorithm results to a plurality of predetermined threshold values. 23.The device of claim 22, wherein the processor is further configured to:determine a reference phase based on the cardiac waveform information;and determine a test phase based on the pressure frequency information,wherein, said distinguishing is based on the pressure frequencyinformation from the test phase and the cardiac waveform informationfrom the reference phase.